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#1
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Unused audio output extension cable
How does the operating system know that an audio cable extension is plugged
in? I have a 20 foot audio extension cable which is just male on one end and female on the other. If I plug in a headphone into that extension cable the sound comes out the headphones and not out the computer speakers. When I just plug in the extension cable, the sound stops coming out of the speakers. How does the OS know that an (unused) audio cable is plugged in? |
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#2
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Unused audio output extension cable
On Tue, 10 Sep 2019 11:10:53 -0400, BillAhearn
wrote: How does the operating system know that an audio cable extension is plugged in? I have a 20 foot audio extension cable which is just male on one end and female on the other. If I plug in a headphone into that extension cable the sound comes out the headphones and not out the computer speakers. When I just plug in the extension cable, the sound stops coming out of the speakers. How does the OS know that an (unused) audio cable is plugged in? It monitors the impedance of the output or input. |
#3
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Unused audio output extension cable
BillAhearn wrote:
How does the operating system know that an audio cable extension is plugged in? I have a 20 foot audio extension cable which is just male on one end and female on the other. If I plug in a headphone into that extension cable the sound comes out the headphones and not out the computer speakers. When I just plug in the extension cable, the sound stops coming out of the speakers. How does the OS know that an (unused) audio cable is plugged in? On a RealTek HDAudio chip, the "standard" method is jack side-contact. The "stack" on the back of the computer, can feel when the plug is inserted and that causes a switch closure. The standard for 48 pin HDAudio chips, has a scheme whereby two pins on the package, can sense the status of eight jacks total. (The switch closures are encoded and sensed by a crude ADC.) The RealTek chip does not know whether the load is a 32 ohm headphone or a 10K ohm audio input from an amplified speaker. It will put up a dialog asking for confirmation. A SoundMax HDaudio chip supports two methods. It has the side contact sensing like all other brands. However, it also has its own unique method. It applies a 25KHz AC signal to the jacks to sense current flow (at 25KHz) and work out the impedance of the load. That product family knows the difference between a 32 ohm headphone and a 10K ohm amplifier, all by itself. It could tell if a "remote load" was plugged into the end of your extension cable. ******* It seems some RealTek chip in this thread, does now have a sensor. But the method would have to be different enough, to not be a patent violation (on the SoundMax method). Due to the relatively small range of measurements it offers, my suspicion is they're measuring the current flow used by the output pad driving LineOut or similar. https://www.reddit.com/r/audioengine...eeps_changing/ Since they're talking about "output sensing" and not "I/O sensing", we don't know whether that RealTek also can sense input types. ******* When impedance sensing is involved, plugging a headphone into the remote cable, should be the only time the speakers are muted. If a solution only has "side contact detection", then as soon as the extension cable is plugged in, the speakers will be muted the whole time. Without actual impedance measurement, the chip can't tell whether a "remote load" is present or not. And even when these techniques are present, the datasheet may not properly delve into the details. Some computers do not have the right kind of jacks with the side-contact on them, in which case "YMMV" :-/ Paul |
#4
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Unused audio output extension cable
Bill,
How does the operating system know that an audio cable extension is plugged in? Take a look at this image. I think you wil get the idea. https://www.cui.com/image/getimage/9166 ( https://www.cui.com/blog/understandi...and-schematics ) Regards, Rudy Wieser P.s. It would be a bit more difficult to check if a headphone was plugged into the /extension cord/ or not. Not that difficult though: it could just put a small bit of current into the cable (posibly at a frequency below 20 Hz), and see if it comes back. If not, no headphones. |
#5
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Unused audio output extension cable
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#6
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Unused audio output extension cable
J. P. Gilliver (John) wrote:
In message , writes: On Tue, 10 Sep 2019 11:10:53 -0400, BillAhearn wrote: How does the operating system know that an audio cable extension is plugged in? I have a 20 foot audio extension cable which is just male on one end and female on the other. If I plug in a headphone into that extension cable the sound comes out the headphones and not out the computer speakers. When I just plug in the extension cable, the sound stops coming out of the speakers. How does the OS know that an (unused) audio cable is plugged in? It monitors the impedance of the output or input. Impedance checking wouldn't work with nothing plugged into the other end of the cable. (Well, very clever impedance checking might, of the sort used for finding where the break is in a cable, but not the sort I'd expect in computer audio circuitry.) It's probably a switch in the socket that detects something being plugged in - probably detected by the audio chip and switched electronically, as described by Paul, but it _could_ be just the mechanical type of switch as described by Rudy - in the same way headphone/earphone sockets have muted the speaker on plugging in the headphone/earphone (or anything else) since at least 1960s transistor radios, probably longer ago. No OS intervention needed! AC'97 used two contacts (stereo) in the jack, to direct the LineOut signals where appropriate. If a headphone was plugged into the Front Panel headphone jack, the plug would cause the contacts to open so that the signal could not flow via "FP_Return" and get to the computer speakers via LineOut jack. This is a DPDT mechanical switch function. This allows one DAC to support two jacks. If the front headphones were not using the signals, then the signals were looped to the lime green LineOut on the back of the computer. Whereas HDAudio has enough output channels for everything. The front headphone jack has its own DAC. There's no need to share with LineOut. The side contact on the jack, is a logic indicator. Usage of the front headphones can still cause the speakers to be muted, but this is a digital function. In fact, some HDAudio chips, in the driver, support enabling two headphone amps at the same time, for a total of four channels of output. This allows two people to listen to different music feeds (this requires the right kind of application, like something in the WinAmp class). The differences between the two schemes are summarized here in picture form. https://www.sevenforums.com/sound-au...l-layouts.html HDAudio has signals for 8 jacks. Headphone and Mic on the front. 7.1 audio out on the back (4 jacks), MicIn, LineIn on the back. The generic pinout is 48 pins. If a "cheesy" laptop HDAudio chip is used, a large number of pins are NC. A top end HDAudio chip uses all the pins and supports the 8 jacks. With AC'97, fewer jacks were provided, so some multiplexing was needed here and there. AC'97 used mechanical switching. HDAudio uses a single side contact per jack, and that is a digital logic indication (plug is in/plug is not in). The driver uses the digital logic indication, to control which channels are enabled. Classical speaker muting can be implemented in the driver, using the front panel headphone jack and its logic indicating signal. Paul |
#7
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Unused audio output extension cable
In message , Paul
writes: [usual excellent detailed Paul explanation/description] Paul Then there's the case of microphone input (often pink), which usually accepts a three-connection (tip, ring, body) plug, but it isn't necessarily stereo - the third may be wired to provide the bias voltage for electret microphones. I had one laptop whose only audio input (_not_ colour-coded) was a microphone one, which presented as stereo in software, but was mono (same signal appeared on both channels). It wouldn't surprise me if some systems automatically detect whether what's plugged in is stereo, mono electret, or mono dynamic (probably rare). -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf "Gentlemen, you can't fight in he this is the war room!" (Dr. Strangelove) |
#8
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Unused audio output extension cable
J. P. Gilliver (John) wrote:
In message , Paul writes: [usual excellent detailed Paul explanation/description] Paul Then there's the case of microphone input (often pink), which usually accepts a three-connection (tip, ring, body) plug, but it isn't necessarily stereo - the third may be wired to provide the bias voltage for electret microphones. I had one laptop whose only audio input (_not_ colour-coded) was a microphone one, which presented as stereo in software, but was mono (same signal appeared on both channels). It wouldn't surprise me if some systems automatically detect whether what's plugged in is stereo, mono electret, or mono dynamic (probably rare). Tip - mono signal in Ring - electret DC bias Sleeve - GND but on the microphone end in that case, they short tip to ring when an electret is used. Whereas a dynamic (moving coil) mono microphone, would not touch Ring and would only use Tip. Naturally, some dynamic microphones predate personal computers and use the "mono" plug design (tip and sleeve). or on a stereo setup Tip - Left Input (AC) plus electret DC bias for this channel Ring - Right Input (AC) plus electret DC bias for this channel Sleeve - GND and in that case, the microphone isn't likely to be a dual dynamic one. And the amount of current the resistor for the electret provides, isn't "supposed" to be sufficient to saturate a moving coil. YMMV of course. It's been a long time since I had a moving coil microphone, as they need too much gain for computer audio systems to use one. Like a moving coil on a vinyl record player might only be 2-3mV or so, and it's a bit much to expect the gain on cheap AC'97 or HDAudio to work with that directly. Nothing prevents more expensive kit with "preamps" fitted, from doing it. Carrying electret bias separately, is intended as a means to give best results with a variety of input types. But they suspend that notion when dealing with stereo-capable mic jacks. If you have a dynamic mic with its own amplifier box, the amplifier has no trouble "pushing around the weak electret resistor". The amplifier has a low enough output impedance, to overpower it. I have more microphones that don't work, versus microphones that work. The one that works, has a "hard" power source and has its own four pin preamp chip. And I can actually dictate with it. There's enough signal. There seems to be some kind of intent, that your microphone won't work... :-) I blame the Illuminati. Paul |
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